Herpes simplex virus is a large double-stranded DNA containing virus whose genome encodes in excess of 70 proteins. The genes encoding these proteins are temporally regulated in a cascade fashion. The interaction of cis-acting signals and trans-acting proteins orchestrates the timing of gene expression. The virus encodes five immediate early (alpha) gene products. One of these, ICPO, is a potent gratuitous inducer of a wide variety of Pol II promoters. The protein is not obligatorily required for replication of virus in cultured cells. However, its presences does have a profound influence on both temporal and abundance controls of mRNA. In addition, expression of ICPO alone is sufficient to reactivate latent herpes simple type 2 in an in vitro model of latency. The goals of this project are to use molecular genetics in combination with classical biochemical techniques and the two - hybrid approach to decipher the functions of ICPO. Preliminary characterization of the protein strongly supports the idea that ICPO exists as a multimer in solution. Genetic analyses demonstrate that the protein is transdominant further supporting the possibility insertion and deletion mutants in the gene encoding ICPO along with a variety of ways of introducing these altered coding sequences into cells. These tools will be used to determine the contribution of specific domains in the protein to such functions as multimerization and transactivation. These studies should provide us with detailed information about how this protein functions in the life cycle of the virus and what it interacts with.